The present invention relates to a membrane of silicon carbide for X-ray lithography and a method for the preparation thereof. More particularly, the invention relates to a membrane of silicon carbide suitable as a masking film in X-ray lithography capable of withstanding intense irradiation with synchrotron radiation or electron beams as a powerful X-ray source.
Known masking materials for X-ray lithography typical in the prior art include (.alpha.-boron nitride):H, referred to as .alpha.-BN:H hereinbelow, disclosed in Japanese Patent Kohyo 55-500707, silicon nitride SiN disclosed in Japanese Patent Kokai 59-116750, polyimide resins disclosed in U.S. Pat. No. 4,037,111 and the like. None of these prior art membrane materials is quite satisfactory for the purpose due to the possible changes caused in the residual tensile stress when the membrane is irradiated with high energy beams such as synchrotron radiation as is reported in "30th International Symposium on Electron, Ion and Photon Beams", May 27-30, 1986, by W. A. Johnson, et al. On the other hand, silicon carbide is studied as a masking material. A silicon carbide film formed by the plasma-excited chemical vapor deposition method, referred to as the PECVD method hereinbelow, in a gaseous atmosphere of silane SiH.sub.4 and methane CH.sub.4, however, unavoidably contains a considerable amount of hydrogen so that the silicon carbide membrane prepared from such a vapor-deposited film contains a large number of defects and is subject to changes in the stress under irradiation with high-energy beams leading to formation of pinholes so that satisfactory membranes can hardly be prepared therefrom. Further, silicon carbide masks formed by the microwave ECR PECVD method are also disadvantageous due to the high content of hydrogen so as not to be free from the problem of a change in the stress under irradiation with high-energy beams.